This application claims priority to Italian Application Serial No. M099A000213 filed Oct. 7, 1999, the disclosure of which is incorporated herein by reference.
The present invention relates to a dielectric pipe joint, particularly for underground pipes.
Several conventional kinds of dielectric joint for mutually joining in a linear fashion pipes are usually made of steel and are designed for being buried and used to convey gas, water and other substances.
These joints are adapted to withstand, over time, the wear produced not only by natural atmospheric agents but also, and most importantly, by so-called stray currents, which are electrical phenomena that are present in the ground and discharge onto the pipes, because they are made of metal, gradually eroding their structural integrity.
Currently, conventional joints are composed of a coupling between a male head of one end of a pipe segment and by a complementary female head which is shaped so as to accommodate the male head.
The male head forms a protruding annular collar which, once inserted in the female head, forms, together with the inner wall of the female head, a receptacle for accommodating a sealing gasket made of elastomeric material, to be interposed between the two heads in order to electrically insulate them.
When the gasket is positioned, the mouth of the complementary female head is folded in an annular fashion onto the pipe with a male head so as to stabilize the coupling and make it monolithic, and any gap remaining between the heads is closed by pouring epoxy resin which sets.
As an alternative, in order to stabilize the coupling, a circular sleeve is welded inside the female head, its height being such that it does not protrude from the head yet can press on the annular collar of the male head, retaining it.
In this case also, a bead of resin is applied in order to close hermetically the resulting joint.
To complete the above-described dielectric coupling, a coat of insulating lacquer is also applied inside the two pipes, particularly in their head regions, so as to eliminate any possible form of electrically active bridge caused by infiltrations and moisture.
However, due to the limited length of the female head and to the proximity between the folded edge of the mouth of the head or of the circular sleeve and the outer surface of the male pipe, or due to imperfect application of the sealing bead of resin and of the internal coating of the pipes, electrical transmission between said heads and therefore between the pipes often persists.
Moreover, the mechanical stresses generated in the soil tend to break up the monolithic nature of the joints, compressing and sometimes damaging the separation gaskets until the metallic portions of the two mating pipes make mutual direct contact, further worsening the damaging flow of electricity.
The aim of the present invention is to solve the above-mentioned problems of the prior art, by providing a dielectric joint for pipes, particularly for underground pipes, which radically eliminates the defects of the prior art, ensuring complete insulation from stray currents over time and even in case of significant mechanical stresses.
This aim and other objects which will become better apparent hereinafter are achieved by a dielectric joint for pipes, particularly for underground pipes, which comprises a male head of a first pipe which enters a mating and mutually opposite cup-shaped female head of a second pipe, a sealing insulating means being interposed between said pipes, characterized in that said sealing insulating means is externally extended on said first pipe by an extent which reaches beyond the inlet edge of said female head and internally forms a tight-fitting cladding of said first and second pipes for a longitudinal extent which is at least equal to the overall length of the joint.